1. Field of Invention
The present invention refers to an oil control ring formed by a ferrous body up to 2.0 millimeters high, idealized for internal combustion engines and which permits an improved distribution of contact pressure and consequently oil scraping, given the association of its constructive design and elastic characteristics of its material base and/or of the assistance of the elastic expansion elements, thus providing better conformability of the ring with the cylinder wall.
2. Description of Related Art
The internal combustion engines are energy transforming mechanisms used by the vast majority of automotive vehicles, and basically comprise two main parts: one or more cylinder heads and the engine block. At the base of the cylinder head(s) are located the combustion chambers (in diesel engines in general the combustion chambers are heads of the pistons) and in the block are located the cylinders and the crankshaft combination. The rotary assembly is comprised of piston(s), rod(s) and the crankshaft.
The engine converts the energy produced by the combustion of the mixture (fuel and air) in the combustion chambers into mechanical energy capable of generating movement to the wheels.
As the driving force needed to move the automobile comes from the burning of the air/fuel mixture in the combustion chamber, and in order to ensure a homogenous combustion and without burning oil and also to avoid the excess passage of gases from the cylinder to the carter, it is necessary to use rings to ensure good sealing of the gap existing between the piston and the cylinder wall.
Normally, three rings are used, of which two are compression rings and one an oil ring. The compression rings are to prevent the combustion gases from entering the carter and the oil ring is to scrape the excess oil from the cylinder wall and return it to the carter.
Another important function of the rings is to act as heat transmission bridge from the piston to the cylinder wall/casing where the heat dissipates through the cooling system.
The oil rings may be comprised by one, two or three pieces, the two latter types being most commonly used in internal combustion engines. As main characteristics, the one-piece ring uses the elastic properties inherent to the material base in order to meet the expansion force requested for the application, whereas the two-piece ring basically comprises a body and an elastic element and the three-piece ring basically comprises a support body and two ring segments to serve the same purpose.
Currently, the oil rings found in the state of the art have cracks or holes distributed along the peripheral cross section of the body. The function of these cracks or holes is to drain off the excess oil accumulated between the two outer work faces of the ring and increase its flexibility by reducing the firmness of the cross section that contains the cracks, providing greater conformability of the part/combination in relation to the cylinder wall.
However, today, spurred by the drive for greater energy efficiency, engine design trends have moved towards the manufacture of smaller engines, with the reduction of losses in power by friction. To accompany these developments, the height of oil rings have become ever reduced, as well as smaller loads and/or expansion force.
Furthermore, with the trends of reducing attrition in the working of the engine, it is possible to maintain an appropriate contact pressure on the interface ring/cylinder, reducing the ring contact area, even under the actuation of reduced expansion loads. Yet, difficulties in manufacturing, handling of parts and even a potential breakage in the work are some obstacles that must be overcome in projects that are designed to reduce the contact area of the oil control rings.
The ring defined in Brazilian patent application PI 9202268 is designed to solve the problem of reducing the contact area using pear-shaped contact surface profiles.
In contrast, the object of patent U.S. Pat. No. 7,117,594 is designed to solve the above-mentioned problem by using a stepped contact surface profile, in the form of steps.
In any case, the design changes associated to this trend of de-creasing height and load, as proposed in the state of the art, may also bring with them other undesirable effects, such as the difference in flexibility between the regions having cracks or not along the cross section of the ring thus enabling a variation of contact pressure applied to the cylinder wall that may generate an insufficient or unequal contact between the ring and the cylinder wall and even the elastic element in relation to the ring in the case of two-piece rings.
North American patent U.S. Pat. No. 6,454,271 describes a combined oil ring, without holes or cracks in the cross section, with an I-shaped body and which uses a rectangular or trapezoidal expander with lower axial height and still capable of achieving high pressure levels, using the removal of the oil drainage areas to enable the construction of the proposed design. Japanese patent application JP 2007170455 describes a two-part oil ring that has reduced spacing of the peripheral cross section (0.6 millimeters or less), where the elimination of the oil drainage areas permits greater constructive firmness of the ring.
Document US2004/021270 refers to a two piece oil control ring comprising a ring body formed into a generally “M” or “I” shaped section with an annular groove on an inside surface of the ring body and a coiled expander attached in the annular groove of the ring body for resiliently urging the ring body toward an inner wall of a cylinder.
The ring body is made of stainless steel that contains chromium of 3.0 to 13.0 weight % with the outer and inner circumferential surfaces covered with nitrided layers. Circular ratio of an outer edge length to an inner edge length in the cross section of the ring body is in a range between 1.08 and 1.32 to keep precise peripheral circularity of the ring body so that the nitrided layers survive lapping of the ring body.
Such patent application, however, does not reveal some important characteristics of the present oil control ring, like at least one contact surface flat, substantially parallel to the cylinder wall and formed by a removal of approximately 25 μm of a triangular end, or the slanted faces of upper and lower rails positioned facing each other.
Document JP 2005 291003 refers to a an odd-form wire rod with a groove with a width of 2 millimeters or less and with a thickness of 2 millimeters or less which can mold an oil ring suitable for a small-sized internal combustion engine. The odd-form wire rod with the groove is characterized in that the width of the rail part sliding surface is not reduced because of grinding processing which makes the surface that is in contact with a ring groove of the piston parallel. The clearance between the extended base lines of the surfaces on both sides which become the surfaces that come into contact with the ring groove of the piston and the outer corner part of the rail part is made not less than 0.08 millimeters each.
This patent application also does not reveal some important characteristics of the present oil control ring, like at least one contact surface flat, substantially parallel to the cylinder wall and formed by a removal of approximately 25 μm of a triangular end, or the slanted faces of upper and lower rails positioned facing each other.
Hence, it is noted that there has not yet been developed an oil control ring that has a maximum thickness of up to 2.0 millimeters and with the peripheral cross section solid, that is, that has no holes or cracks for the oil flow, in order to solve the difficulties of conformation of the ring surfaces in relation to the cylinder wall and/or of the ring in relation to the elastic element if such is used, also being capable of maintaining suitable levels of contact pressure, even under low load due to the use of a profile that provides reduced contact of the ring with the cylinder interface.